Non ablative, state changeable, optical data storage systems record information in a state changeable material that is switchable between at least two detectable states by the application of energy thereto, for example, the application of projected beam energy such as optical energy, particle beam energy or the like.
The state changeable optical data storage material is present in an optical data storage device having a structure such that the optical data storage material is supported by a substrate and encapsulated in encapsulants. The encapsulants may include anti-ablation materials and layers, thermal insulating materials and layers, anti-reflection layers between the projected beam source and the data storage medium, reflective layers between the optical data storage medium and the substrate, and the like. Various layers may perform more than one of these functions. For example, the anti-reflection layers may also be thermal insulating layers. The thicknesses of the layers, including the layer of state changeable data storage material, are optimized whereby to minimize the energy necessary for state change while retaining the high contrast ratio, high signal to noise ratio, and high stability of the state changeable data storage material.
The state changeable material is a material capable of being switched from one detectable state to another detectable state by the application of projected beam energy thereto. State changeable materials are such that the detectable states may differ in their morphology, surface topography, relative degree of order, relative degree of disorder, electrical properties, and/or optical properties, e.g., reflectivity and/or refractive index, and that the state of the material be detectable, e.g., by the electrical conductivity, electrical resistivity, optical transmissivity, optical absorption, optical reflectivity and any combination thereof.
Tellurium based materials have been utilized as phase changeable memory materials. This effect is described, for example, in J. Feinleib, J. deNeufville, S. C. Moss, and S. R. Ovshinsky, "Rapid Reversible Light-Induced Crystallination of Amorphous Semiconductors," Appl. Phys. Lett., Vol. 18(6), pages 254-257 (Mar. 15, 1971), and in U.S. Pat. No. 3,530,441 to S. R. Ovshinsky for Method and Apparatus For Storing And Retrieving Of Information. A recent description of tellurium-germanium-tin systems, without oxygen, is in M. Chen, K. A. Rubin, V. Marrello, U. G. Gerber, and V. B. Jipson, "Reversibility And Stability of Tellurium Alloys For Optical Data Storage," Appl. Phys. Lett., Vol. 46(8), pages 734-736 (Apr. 15, 1985). A recent description of tellurium-germanium-tin systems with oxygen is in M. Takanaga, N. Yamada, S. Ohara, K. Nishiuchi, M. Nagashima, T. Kashibara, S. Nakamura, and T. Yamashita, "New Optical Erasable Medium Using Tellurium Suboxide Thin Film," Proceedings, SPIE Conference on Optical Data Storage, Arlington, Va., 1983, pages 173-177.
Prior art deposition techniques include evaporative deposition. However, disordered memory materials deposited by evaporative deposition have been found to suffer from concentration gradients with respect to deposition depth. This is not altogether remedied by "initializing." That is, while the memory material must be initialized as described, for example, in the commonly assigned copending U.S. Application Ser. No. 667,294, filed Nov. 1, 1984, of Rosa Young and Napoleon Formigoni for Method Of Forming An Optical Data Storage Device, the vertical gradients may not be eliminated thereby. As described therein, the memory material must be conditioned, formed, initialized, or otherwise prepared to receive data if the data is going to be recorded in a disordered ("binary") state. Initialization, i.e. formation, requires the conversion of the phase changeable data storage material from the as deposited disordered state to a stable system switchable between a state corresponding to binary 1 and state corresponding to binary "0," with history invariant cycling properties.
Present systems are multiphase systems where the ordering phenomena includes a plurality of solid state reactions and/or interactions to convert a system of predominantly disordered materials to a system of ordered and disordered materials, and where the vitrification phenomena includes solid-solid, solid-liquid, and liquid-liquid reactions and/or interactions, including reactions and/or interactions at phase interfaces, whereby to convert a system of disordered and ordered components to a system of predominantly disordered components. The above phase separations occur over relatively small distances with intimate interlocking of the phases and gross structural discrimination.
Exemplary of this reacting system is the reaction of the prior art disordered germanium-tellurium-oxygen systems under "crystallizing" conditions to form germanium oxides, including suboxides and non-stochiometric oxides, tellurium, and different germanium-tellurium compounds, where the tellurium is crystalline.